Compact lasers with narrow linewidth are known and used in applications such as molecular and bio-molecular spectroscopy, medical diagnostic systems, high resolution optical ranging, coherent optical communication systems, imaging, optical phased arrays, mm-wave and THz signal generation, electro-optical oscillators, sensing, and the like.
Commercially available Sub-KHz fiber laser linewidths have been achieved at the expense of small wall-plug efficiency, weak tunability, and undesired mode hoping characteristic. Using a conventional feedback technique to cancel phase noise over a large frequency bandwidth often results in feedback loop instability. Accordingly, a need continues to exist for an optical signal linewidth reduction system that overcomes the shortcomings of the conventional linewidth reduction systems.